1. Field of the Invention
This invention relates to a new process for the catalytic hydrogenation of fatty acid methyl ester mixtures using particulate and/or granulated catalysts containing copper chromite under pressures in the range from 100 to 300 bar.
2. Description of Related Art
Fatty alcohols, i.e., predominantly linear, monofunctional alcohols having chain lengths of 8 and more carbon atoms, and their production are described in detail in the literature, for example in Ullmanns Encyklopaedie der technischen Chemie, 4th Edition, Vol. 11, pages 427 to 445. A preferred starting material for their production are the fatty acids and fatty acid mixtures occurring in natural fats and/or oils which may be converted into fatty alcohols of corresponding chain length by catalytic hydrogenation. Through the use of the fatty acids to be reduced in the form of their methyl esters, the catalysts in particular are protected against aggressive attack by the free carboxyl group, so that industrial processes can be operated for sufficiently long periods with satisfactory volume-time yields. Today, therefore, the predominant quantity of native fatty alcohols is produced from fatty acid methyl esters by the gas-phase hydrogenation process in which the distilled methyl esters are passed in the vapor phase, together with a large excess of hydrogen, over a fixed bed of copper-containing mixed oxide catalysts, such as, for example, copper chromite spinel catalysts, at temperatures above 200.degree. C. and under pressures of from about 250 to 300 bar.
The copper-mixed oxide catalysts obtained by co-precipitation via the wet route are used as particulate catalysts or extrudates and before use are generally reduced in the plant or installation.
According to the relevant patent literature, fatty acid esters, more especially fatty acid methyl esters, and free fatty acids are therefore simultaneously used as starting materials for the hydrogenation reaction to saturated and/or unsaturated fatty alcohols, for example, as described in German Patent Publications DE-PSS 965 236, 10 05 497, 25 13 377 and 26 13 226. U.S. Pat. Nos. 4,113,662, 4,482,766, and 4,199,479 as well as Indian Patent 124510 also describe pertinent process features. As far as industrial application is concerned, the proposals mentioned are evaluated entirely differently according to whether the fatty acid esters or the free fatty acids are used as starting material for the hydrogenation.
According to the present state of the hydrogenation art, the methyl esters are separated by distillation, after transesterification of the oils and fats and after separation of the glycerol, into a boiling cut in the 8 to 10 carbon chain range and into a boiling cut in the 12 to 18 carbon chain range to enable the hydrocarbons automatically accumulating to be removed during the subsequent hydrogenation of the methyl esters. The two fractions are separately hydrogenated, the quality-reducing hydrocarbons being distilled off overhead. Since the boiling ranges of the hydrocarbons overlap those of the short-chain fatty alcohols, the fatty acid methyl esters must be separated according to the present state of the art. In addition, the reaction velocity in the hydrogenation of short-chain fatty acid methyl esters is lower than in the hydrogenation of long-chain fatty acid methyl esters. Accordingly, fatty acid methyl esters in the 14 to 16 carbon chain range are overhydrogenated when co-hydrogenated with shorter-chain fatty acid methyl esters. The carbon chain ranges separated are normally hydrogenated at different space flow velocities.